The technical and patent literature relating to the construction and operation of aluminium smelting cells invariably supports the firmly entrenched belief that an aluminium smelting cell must operate with a stable ledge of frozen electrolyte material protecting the regions of the side wall of the cell contacted by the electrolyte bath and the molten aluminium produced thereby against the destructive action of the electrolyte and aluminium melts. For example in "Light Metals" 1979, Pages 475 to 492, Peacey & Medlin, describe the desirability of parameters of cell side wall design which promote the formation of a good ledge, while in "Light Metals" 1983, Pages 415 to 477, various authors, describe the factors necessary for the maintenance of a stable side ledge structure.
In the patent literature, the desirability of promoting an adequate side ledge is described in many prior art patents. For example, in U.S. Pat. No. 4,608,135 Brown uses artificial cooling of the side wall to induce the formation of an adequate side edge, while in U.S. Pat. No. 4,466,995 Boxall et al, describes a cell structure which controls the size of the side wall ledge but nevertheless indicates that the formation of such a ledge is essential.
Notwithstanding the widely recognized need for adequate ledge in the operation of known aluminium smelting cells, the advantages of operating a cell without a ledge are well understood but have not thus far been able to be achieved other than by substantial reductions in cell operating temperatures coupled with substantial modifications to the bath chemistry (see U.S. Pat. No. 5,006,209, Beck et al).